Renal arterial duplex Doppler ultrasound in dogs with urinary obstruction

Recent clinical studies using duplex Doppler sonography identified an alteration in renal arterial blood flow in obstructed hydronephrotic kidneys that reportedly can be used to distinguish obstructive from nonobstructive collecting system dilatation. We attempted to verify these clinical findings and establish the temporal relationship of the alteration in the Doppler spectrum to the onset of urinary obstruction by evaluating surgically induced urinary obstruction in dogs. We performed laparotomies on 11 dogs, with the left ureter isolated and ligated in five dogs, and left intact in six dogs (control group). Duplex Doppler examination of the left renal arteries performed nine times during the first postoperative month identified a statistically significant difference (p less than .05) in the Doppler resistive index calculation between the two groups on days 1, 2, 4, and week 4. A resistive index discriminatory threshold of 0.7 (greater than 0.7, obstructed; less than 0.7, nonobstructed) produced a test sensitivity of 74% and specificity of 77%. We conclude from our study that renal arterial duplex Doppler sonography can detect a change in renal perfusion as a result of urinary obstruction and that this change can be detected as early as 24 hours after obstruction. However, high false-positive and false-negative rates may limit the ability of this modality to reliably distinguish obstructive from nonobstructive collecting system dilatation.